Hybrid wireless cellular communications devices (WCDs) are capable of communicating on both cellular networks and in broadband wireless networks, such as, 802.11 protocol-based or WLAN-based networks. As the WCD moves physically and/or the fading channel changes due to subtle variations in the complexity of the physical surroundings, the WCD supports a specific set of logical decision-making capabilities which determine how a cell and/or network will be selected. Generally, a hybrid WCD may detect and select one network or the other, or both.
Broadband wireless communication protocols support radio resource management techniques for detecting one or more operating frequencies and access points. A cellular system, such as Global System for Mobile telecommunication (GSM), however, has little in common with alternate radio access interfaces, for example, a standardized WLAN like 802.11 or other wireless technologies, capable of meeting the requirements for operation in unlicensed spectrum. The differences in radio behavior result primarily from differences in operating bandwidth, power limitations for unlicensed operation, Medium Access Control (MAC) protocol (either reservation-based or contention-based) designed to handle different predominant traffic types, frequency range of operation and accordingly, the resulting difference in radio propagation characteristics and the interference environment for licensed/unlicensed operation.
When a dual mode WCD moves from a cell where it is communicating with a Mobile Switching Center (MSC) of a GSM network to another cell where a UMA network is the preferred network, the WCD operates in a UMA preferred mode. The WCD will attempt to handover to an Unlicensed Network Controller (UNC) that operates over unlicensed IP spectrum. When a WCD is in a UMA preferred mode of operation, at power up, the WCD scans for access points within a UMA network. According to some specifications, when a WCD is operating in a UMA preferred mode of operation, the WCD should be capable of discovering or detecting an access point of the UMA network within a short time (e.g., 15 seconds) after entering into it, and associating with the UMA network within another short time (e.g., 15 to 30 seconds) after detecting the access point.
According to one approach, the WCD continuously scans for access points to discover its preferred networks. The host baseband processor of the WCD wakes up every predetermined scanning interval to continuously scan for access points. The host baseband processor then goes to sleep after initiating the scan until the next scanning interval when the host processor is awoken to scan again. Scan results are returned to the host baseband processor if an access point is detected. However, executing this entire scan procedure at such short time intervals (e.g., every 15-20 seconds) can in many cases unnecessarily wakeup the host baseband processor to process scan information for access points that may not be available for association. The two processor blocks and their associated software blocks are awakened or activated during each scanning interval. This requires a large number of commands and a great deal of communication between the various sub-modules of the host baseband processor, which in turn results in a significant amount of communication overhead being passed between the various modules. Using this approach to detect an access point within a UMA network can consume substantial current and battery power.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below.